You can access a majority of the personalized Yahoo content with your browser on the Axim. You can read and send e-mail. You can get stock quotes based on your portofolio but not detailed quotes.
http://pg1.yahoo.com/
I use it all the time with my WiFi card. Nothing like reading e-mail, watching TV and sitting on the couch. :D I wish there were more WiFi hotspots in the neighborhood!
I sync my e-mail with my outlook on my laptop, so I've never tried to set up Outlook to read POP3 or anything else. So, I am not sure if or how that would work with Yahoo. I do know Yahoo will work with a POP3 client if you upgrade you e-mail account.